Faucet Dripping - Next Step?

I think that I have a Moen in my small downstairs half bath. A piece on it had the number 100484. Don't know if that means anything. I'm obviously a novice.

Anyway, it's been on a slow drip for a while now. I got it apart as far as this pic shows. Now what? I can't seem to go any further. What's the typical issue with this model and how does one fix it?

Thanks in advance for the help!

Update: Just did some research. This looks to be a moen 4520.

Found the instructions and got the cartridge out. Just FYI for anyone.

http://www.moen.com/shared/pdf/instruction_sheets/INS192.pdf